RNAi (RNA interference) and antisense (AS) strategies consist in silencing the expression of a target gene by the use of nucleic acids which allow the degradation or the translational arrest of mRNA target. New antisense applications (exon skipping, alternative splicing correction), by masking the mutation responsible for an alternative splicing default, have permitted the synthesis of a functional protein. Aptamers are nucleic acids capable of interacting with a target protein and down regulating its synthesis. The discovery of all these nucleic acids, and more recently siRNA, miRNA and RNAa has opened wide perspectives in therapeutics for the treatment of diseases like genetic diseases, cancers, neurodegenerative diseases, infectious and inflammatory diseases or to block cell proliferation and diseases caused thereby.
However, these molecules are unstable in biological fluids, in vitro and in vivo, they display a poor intracellular penetration and low bioavailability. These critical drawbacks have limited their use in therapeutics. As a result, clinical applications of said nucleic acids have required chemical modifications with the aim of retaining their capacity to knockdown protein expression while increasing stability and cellular penetration. Research groups have also applied the nanotechnology approach to improve their delivery, to overcome most barriers that hampered the development of nucleic acids delivery based therapies. To improve bioavailability, many researchers have also attempted to use alternative administration routes: ocular, skin, oral, intramuscular. Those attempts have not been totally satisfactory so far. For instance, some of these attempts, more specifically assays with nucleic acids in liposome carriers have stimulated immune response.
The inventors have previously uncovered that complexes could be obtained from two organic compounds isolated from plant extracts and respectively constituted of sitosterol and acylglycerols and hydrosoluble therapeutic agents (WO2006/048772), these complexes being particularly effective agents as trans mucosal vectors of said therapeutic agents. Such vectorization of hydrosoluble therapeutic agents affords an important decrease of the administered amounts compared to their administration in the absence of micelles as previously described.
Said complexes have been shown effective to vectorize hydrosoluble therapeutic agents by mucosal immediate administration. The stability of microemulsions containing therapeutic agents is not however always satisfactory to allow their development as delivery systems for drugs and/or dietetic compounds for example. Such development requires formulations to be stable over longer periods of time, for instance over several weeks or months at room temperature.
It is an object of the present invention to overcome disadvantages of the prior art. There is an obvious need for a safe and efficient nucleic acids therapeutic strategy, and in particular for new tools that are able to achieve efficient gene expression modulation based therapy. More particularly, it is an object of the invention to provide a drug delivery system comprising a nucleic acid, in particular an oligonucleotide, which can be for instance administered mucosally, giving rise to a satisfactory drug bioavailability in an active form.
Incorporation of a phospholipid or a sphingolipid, in particular in specific amounts, in the formulation of microemulsions comprising high doses of nucleic acid surprisingly triggered an important increase in their stability.
The present invention describes new microemulsions formulations able to vectorize high quantities of nucleic acids, process of preparation and use thereof as delivery systems for drugs and/or dietetic compounds. “High” amounts refer here to amounts sufficient to obtain a therapeutic activity at the human scale, but that remain far lower than the amounts of nucleic acid delivered in absence of complexes.
This formulation advantageously renders possible the control and optimisation of the composition comprising micelles for their use in the pharmaceutical and dietetic fields.